AVO raised the Aviation Color Code to Orange and the Alert Level to Watch yesterday in response to observations of a new lava dome in the summit crater of Cleveland Volcano . New observations from August 2 show that the lava dome has grown from about 40 meters (131 feet) to about 50 meters (164 feet) in diameter since July 29. Weak thermal anomalies were detected in satellite images last night and this morning which is consistent with slow dome growth or a cooling dome.

If dome growth continues, lava flows onto the flanks of the volcano may develop but would not be hazardous to aviation. The presence of the lava dome increases the possibility of an explosive eruption, but does not necessarily indicate that one will occur. Short-lived explosions could produce an ash cloud that exceeds 20,000 ft above sea level. These events can occur without warning and may go undetected in satellite imagery for hours.

Without a real-time seismic network at Cleveland, AVO is unable to track local earthquake activity related to volcanic unrest, provide forecasts of potential eruptions, or confirmation of explosive activity. Low-level ash emissions and elevated surface temperatures such as those observed recently do not necessarily mean a larger eruption is imminent. AVO continues to monitor the volcano using satellite imagery.

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.

VOLCANO ALERT LEVELS

NORMALVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

ADVISORYVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

WATCHVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.

WARNINGHazardous eruption is imminent, underway, or suspected.

AVIATION COLOR CODES

GREENVolcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.

YELLOWVolcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

ORANGEVolcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].

REDEruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].